1. Field of the Invention
The present invention relates to a liquid crystal display apparatus, and more particularly, to a liquid crystal display panel, which has on-off pads formed on a non-display region of a thin film transistor substrate for testing short circuit characteristics of gate lines or data lines, and a liquid crystal display apparatus having the same.
2. Discussion of the Related Art
A liquid crystal display apparatus may comprise a liquid crystal display panel further comprised of an upper substrate having a color filter, a lower substrate having a thin film transistor array, and a liquid crystal layer formed between said substrates and a driving circuit for supplying a driving signal to the liquid crystal display panel. Thus, the liquid crystal display apparatus may have a structure where an array substrate on which thin film transistors are arranged, and a color filter substrate having red, green and blue sub color filters are attached to each other with liquid crystal sealed between them.
Once the substrates are attached together, they are cut in units of liquid crystal display panels each having a display region and a non-display region. Then, each unit is checked for defects.
Next, a grinding process for grinding an edge of the liquid crystal display panel units is carried out.
In a scribing process and grinding process, a shorting bar for static protection and test signal wiring are cut, and then an assembling process for electrically connecting them to a circuit device such as a gate PCB, data PCB, etc. of the liquid crystal display apparatus is carried out.
Referring to FIG. 1, a liquid crystal display panel having a test pad part will be described in detail.
FIG. 1 is a view showing a related art liquid crystal display panel having a test pad part, in which the related art liquid crystal display panel 100 is divided into display parts 110 and non-display parts 120.
Referring to FIG. 1, when a lower thin film transistor substrate on which pixel electrodes are formed, and an upper color filter substrate on which color filter layers are formed are completed, an attachment process for attaching the thin film transistor substrate and the color filter substrate is performed. Thereafter, a cell process is performed. In the cell process, a first scribing process for cutting the attached substrates in a bar shape along a first scribe line is initially performed.
On the liquid crystal display panel 100, formed by cutting the substrates into a bar shape according to the first scribing process, a plurality of display parts 110 and non-display parts 120 are formed. Especially, in the case of a small-size liquid crystal display apparatus, a large number of display parts 110 and non-display parts 120 exist in the liquid crystal display panel 100 cut according to the first scribing process.
Each of the display parts 110 may be comprised of a pixel part 111 used as an active region, a gate pad part 112, a data pad part 113 and a test circuit part 114. Each of the non-display parts 120 is comprised of a test pad part consisting of a gate test pad 121 and a data test pad 122 and a connection terminal 123.
As described above, once the substrates, separated according to the first scribing process, are cut into a bar shape, a liquid crystal injection process is performed.
When the liquid crystal injection process is finished, a second scribing process for cutting along a second scribe line in units of display parts 110 is performed on the liquid crystal display panel 100 cut into each bar type.
When the second scribing process is performed, the liquid crystal display panel is separated into one unit of liquid crystal display having a display part and a non-display part.
The thus-separated liquid crystal display panel 100 is then subjected to a cell testing process for testing a driving state. A gate driving signal and RGB data signals are applied through test signal wiring 124 and test pads 121 and 122 that are formed on the non-display part 120, to thus test a driving state of the display part 110 in the pixel part 111 used as an active region.
The test signal wiring 124 is electrically connected to the data pad part 113 and the gate pad part 112. When a test signal is applied through the test signal wiring 124, a data signal for testing is applied according to the turn-on or turn-off of the thin film transistor TFT formed in the active region 111 of the display part 110, to check if pixels are defective.
The test pad parts 121 and 122 may be classified as a gate test pad part 121 and a data test pad part 122. Each of the test pad parts 121 and 122 may have a plurality of on-off pads 121a, 121b and 121c formed thereon, and the on-off pads 121a, 121b and 121c are electrically connected to each other.
Once the cell testing process is finished, a grinding process is performed to short-circuit the test signal wiring 124. Thus, part of the test signal wiring 124 is formed substantially adjacent to the first scribe line.
Hence, a grinding part (not shown) for short-circuiting the signal wiring 124 is formed at a region substantially adjacent to the first scribe line and the test signal wiring 124. The test signal wiring 124 is ground along with edges of the substrate according to a grinding operation, thereby short-circuiting part of the test signal wiring 124.
FIG. 2A is a view for explaining the occurrence of electrolytic corrosion or other corrosion of on-off pads in the test pad parts 121 and 122 according to the related art. FIG. 2B is a photograph showing electrolytic corrosion or other corrosion occurring on the on-off pads.
Referring to FIG. 2A, the on-off pads 121a, 121b and 121c in the test pad parts 121 and 122 according to the related art are made of Mo or AlNd or the like. Furthermore, a substantially more negative voltage is applied to one of the on-off pads 121a, 121b and 121c than the neighboring on-off pads upon driving the liquid crystal display panel 100, and a subsequent leakage current may cause electrolytic corrosion.
For instance, in a substrate of a COG (Chip On Glass) type, the driving of the liquid crystal display panel is carried out by a signal applied from a source or gate driving circuit (D-IC) 125. For example, the test pad parts 121 and 122 have such a structure in which a signal 127 applied from the driving circuit 125 must be applied to the on-off pads 121a, 121b and 121c along a signal line 126 connected therebetween.
FIG. 2B is a photograph showing electrolytic corrosion or other corrosion occurring on the on-off pads 121a, for example, in the test pad part 121. A problem results in that unintended gate and data signals are applied to the on-off pads 121a, 121b and 121c thus causing electrolytic corrosion or other corrosion of the on-off pads 121a, 121b and 121c. 